Transistor neon driver



March 1, 1960 Filed June 27, 1958 FIG. 1

P 4.7 K 0b IN N R. B. HENNIS .2 Sheets-Sheet 1 TYPE 14 INVENTOR ROBERTB. HENNIS ATTORNEY March 1, 1960 R. B. HENNIS TRANSISTOR NEON DRIVER 2Sheets-Sheet 2 Filed June 27, 1958 Nd E 2 1 A 2 S 25:: Z 55 x;

United. States Patent TRANSISTOR NEON DRIVER Robert B. Hennis,Poughkeepsie, N. assignor to International Business MachinesCorporation, New York, N.Y., a corporation of New York Application June27, 1958, Serial No. 744,978

5 Claims. (01. 315-135 This invention relates to indicator circuits andmore specifically to improved transistor circuits for controlling ordriving visual signal devices or neon indicators to indicate electricalconditions in other circuits.

In the transistor circuits which are replacing vacuum tube circuits inmodern day electronic equipment, the operating potentials are at a'relatively low level. The potentials needed to operate commerciallyavailable neon indicator lamps are at a higher level. The use in aconventional transistor circuit of a potential high enough to operate aneon indicator lamp, might subject the transistor to a potential highenough to cause punchthrough. When punch-through occurs, the transistorno longer functions to produce normal transistor action.

Another difficulty encountered in the design of a transistor circuit foroperating a neon indicator is the fact that commercially available neonlamps have a wide range of firing and extinguishing potentials.

The invention makes use of a pulsating DC. or A.C. voltage on oneterminal of a neon for varying the potential at the terminal by anamount greaterthan the difference between the minimum extinguishingvoltage and the maximum firing voltage of neons. The other terminal canthen be placed at either of two D.C. levels, one of which does not allowthe varying DC. potential across the terminals of the neon to reach theminimum firing voltage, so as to maintain the neon in its ofi condition,and the other of which shifts the reference of this varying DC.potential so that the latter scans from below the minimum extinguishingvoltage to above the maxi mum firing voltage of commercial neons and theneon flickers to appear lit to the eye.

It is an object of this invention to provide an improved transistorcircuit for reliably operating a neon indicator lamp.

Another object of the invention is to provide a transistor circuit forreliably operating a neon glow lamp without subjecting the transistor tounduly high potentials.

Still another object of the invention is to provide a transistor circuitwhich can operate reliably to fire a neon lamp for the full range offiring and extinguishing voltages of commercially available neon lamps.

A further object of the invention is to provide a scanning voltage whichvaries an amount greater than 'the difierence between the minimumextinguishing voltage and the maximum firing voltage of neons.

A still further object of 'the invention is to provide a means foreffectively shifting the reference level of the varying potential acrossa neon lamp from a position where the voltage peak does not reachthefiring potential of the neon to a position where the peak voltage isgreater than the maximum firing voltage and the minimum potential islower than the minimum extinguishing point of commercially availableneon lamps.

Another object of the invention is to provide a trausistor operated neonlamp indicator wherein'the'voltages 2,927,247 Patented Mar. 1, 196i}cially available neon lamps, and yet never apply greater are high enoughto operate inthe' iull'rangepfcomrnerthan the punch-through voltage tothe transistor.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which discloses, by way of example, the principles of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a circuit diagram of the preferred embodiment of theinvention. t Fig. 2 illustrates the voltage conditions in the circuit 0EFig. 1 when the neon is not firing.

Fig. 3 illustrates the voltage conditions in the circuit of Fig. 1 whenthe neon is firing.

Before describing the invention it is necessary to understand some ofthe operating characteristics of present day commercially availabletransistors and neon lamps.

It is well known in the art that a neon lamp will not fire to light upuntil the firing voltage of the neon lamp is reached. Once the neonfires, it operates as a constant voltage device and will continue toremain lit until the extinguishing voltage, which is substantially lowerthan the firing voltage, is reached. Different neon lamps manufacturedunder the same type designation may have different firing andextinguishing voltages. For any particular type designation of neon,there is a fairly well defined range of firing and extinguishingvoltages. ,For example, in the NE- type neon, which is utilized in thepreferred embodiment of the invention, the firing voltage for thedifferent neons may vary from a minimum of 65 volts to a maximum of 90volts. The extinguishing voltage may vary from a minimum of 53 volts toa maximum somewhere below the firing point of the particular neon. Theaverage firing voltage for an NE-75 is approximately volts and theaverage extinguishing voltage is 60 volts.

In the commercially available junction transistors, which are bestsuited for the operation of the preferred embodiment of the invention,the operating voltage usually placed at the collector of the transistorranges between 5 and 20 volts. While there is no reason for going higherin a normal circuit design, these transistors are generally capable ofoperating with a collector voltage of 45 volts. This voltage is too lowto operate the neon lamps. If voltages of greater than 45 volts areused, the problem of punch-through arises.

If the collector voltage of a transistor is increased sufficiently tocause the depletion region of the collector to move entirely through thebase region and at some point contact the emitter region, a relativelylow resistance path between the emitter and collector is established.This phenomenon is known as punch-through breakdown, and is more fullydescribed in the Handbook of Semiconductor Electronics by L. P. Hunter,published in 1956 by McGraw Hill. When punch-through occurs, transistoraction is lost.

A transistor indicator circuit is shown in the patent to J. C. Logue etal., in Patent 2,772,410, issued November 27, 1956. The presentinvention, which is an improvement on that patent, has a circuit whichis operative for the full range of commercially available neons ratherthan for hand picked neon lamps.

One of the problems which is encountered in the circuit of the typeshown in the Logue et al. patent is the reverse current which flowsbetween the base and the collector through the collector resistor duringcut ofi time. This current, known as ICQ eifectively operates to producea voltage drop across the collector resistor. This condition acts tomake a lower voltage available for operating the neon as will be morefully described hereinafter. It is to be understood that this I variessubstantially with changes in temperature and from transistor totransistor in commercially available transistors, and so it is necestotake into account theworst conditions. That is,

if there is a low I' there is a larger voltage applied at sistorcircuitincluding an IBM type I4QPNP' junction I transistor having anemitter electrode 102, a base electrode 10b and a collector electrode100. Thecollector electrode is connected through a 39K ohm resistor $2to a source of '43 voltsD-E. 13 and the collector elecwhichis connectedto a pulsating source of DC. The waveformfor the pulsating source isshown inl-Figs; 2

drops to O. The neon remain in this unlit condition "until terminal 18again goes above +3-7 volts so that there is 80 volts across the, neonand it again fires. The operation then continues irr the same manner aspreviously described. The preferred source used for the pulsating DC.voltage, which is applied to terminal '18 is a 60 cycle input,which'atter being put through a full wave rectifier, beco E s-a: 1'20cycle Wave. Thus,

' the neon would-"go on orice for each cycle of the 120 trade-10c isalsoconnected oranges 150K ohm resistor .14 and a neon glow discharge lamp16to a' terminal 18,

and- 3', and varies from-'0 volts to +57 volts DLC. F'This may be a wellknown type of waveform generated in a full wave rectifier whichhas nofilter at its output. The base 10b is connected through a 4.7K ohmresistor 20' to an input terminal IN, and also through a 18K ohmresistor-22 to a source of +10 volts D-.C. -24.

The indicator circuit ofthe invention is ordinarily uti-- lized toindicate the-stateof other transistor circuits-as described in Logue eta1; patent. found in the output of transistors, especially trigger cir-'cuits, well known in the art varies from O to 5 volts; The neo11= lampof the invention will glow to indicate when the output of the transistorcircuit to which it is' connected is at 0 volts, andwill' not glow' whenthe out.

put of the-transistor circuit is at +5 volts.

When the input signal from-a previous transistor stage" goes'to 5 volts,the voltage at the ;base 10b of the driving' transistor 10 starts to gonegative, and the transistor 10 conducts current from the emitter 102:t'o-the-col-lector 10c. When the driving transistor 10 conducts current,the collector 100 goes to approximately ovens. With The voltage levels;

0 volts on the collector 19c, theneon 16 is efiectively in I acircuitfrom the collector ltl'c-through the 150K. ohm v resistor and the neon16 to the terminal -18.

It can'be seen from 'Figs. 1 and 2; that th'ere will be no currentflowing through the neon, assuming first that there is 0 volts on theterminal 18' and 0 volts at the collector 10c, terminal =18 variesfrom-O to -|-57 volts and thus, the voltage across the neon varies n mmini' mum of '0" volts toa maximum or 57 volts. 'Since this maximumvoltage-is not "enough to fire a NIB-75', even one at the'lowes'tend ofthe range with-a firing voltage V of 65 volts, the neonswill definitelynot be-fired.

When 0' volts are applied at input-terminal the resistors 20 and 22 actas a voltage divider and approximately +2 volts are applied tothe'base'Illb of the driving transistor -10. This positive voltage onthe base of a PNP transistor will cut it OE. With no current flowingfrom the emitter to the collector of the driving transistor 10, the neon16 is 'etl'ectively in a: circuit from the terminal 1 3 through the 39Kresistor, the ISOK ohm resistor and the neon-1 6' to thet'erminal 181' vFig; 3 illustrates the pulsating voltage on terminal -18 and there'is aconstant source of -43 voltsat terminal 13. Taking the average firingvoltage of*80- volts: as the firing voltage, Fig. 3- indicates thatwhen-the voltage across the neon is 80 volts, the neon will fire. --'Fhevoltageacross the neon almost immediately drops to avoltage-just abovethe extinguishing voltage, intheexample, approximately 60 volts; Eventhough the voltage at" team-ariscontinues to rise, the neon hasqaconstant drop-of approximately 60 volts across it. When-"however, thevoltage at terminal18 goes below +1 7 volts (assumin'gpan averageextinguishing voltage of 6 0 volts), the

neon ,i's'exti s gh an th vo taseastos it inalusistely cyclewave. It.thus flickers on and oh at a cycle rate is. fast enough so'that itappears-to be lit to the normal eye. 7 a V v t The importance of apulsating DC. voltage or varying voltage on terminal 18 may' beunderstood an analysis is made of a circuitwhich does notuse the.pulsating DC. current. As has been hereinbefore. described, the

voltage at terminal 13 is limit'e'dto about 45 volts because of thepossibility of transistor punch-through. The

voltageon terminal 18', if it is to "be' D.C;, is limited because itmust below enough to provide an extinguishing v'enagewhenme collector ofthe transistor I 0 'is' at "0 volts. In addition, since the neon must;be fired when the transistor 10 is cut off, the factor caused by I mustbe taken into account. 1'5 flows through resistorIZ and produces'avoltage" drop which may be as high as 10 volts. This further limits: thepotential available to the neon because" it produces aminepositive pointat the collector than 5t 3"volts." The voltage across the neon availablefor firing is the: sum of the'potential at terminals 18 and 13' minusthevoltage drop "du'e to 1 6.

By using the"pulsating" D.C; voltage at terminal 18, the voltage can bemade to-rise high enough to produce firing and low" enough to provideextinguishing. The amount of DC. voltage necessary at terrnihal 13 thenbecomes amount which is' high enough to. shift the pulsating no: voltageat 'terminal' ltltrom just below the extinguishing'point to justabove'the firing point. Therefore, this D.C. voltage does not have to be madeso high, as to cause punch-through of the transistor.

The pulsating P.C.- voltage must vary so that'the differencebetweenits-'m'inimum point'andfits. maximum point is slightly more thanthe difiere'nce between the minimum extinguishing voltage and maximumfiring voltage.- It may be understood 'that'thi s p'uls'atin'g DlC.voltage maybe an A6; ol-za' esuperimposed on a= D.C; ,voltagein a wellknown manner. It can beunder'stood that with this circuit, ifa neonburns 1 out, it can'gbe replaced from commercially available stockwithout worrying about read 'u'sting circuitv'al'ues;

While there have been shown and describedv and pointed out the-fundame1ital novel feat'ur es of the invention as applied to apreferred embodiment; it will be understood that various omissions andsubstitutions and, changes in the forum and details of the":deviceillust r'ated 'ahdin its operation may be mad'e' by those skilled"in the art without departing from the spirit'lof the inyenti'on. -It isthe intention therefore, tobe limited only as indicated by the scope ofthe ifollowing claims:

1. Visual signal apparatus comprising in' combination, .aglowdischarge-lamp having a'-"firing potential and an extinguishingpotentialwithin a predetermined range of values, a; source ofpotential connectedto one terminal of said glow lampxwhich varies periodically'hy'an amountgreater than saidtcpredetermined range, .and means for applying a;unidirectional .potential to; the other .terminal of said glowvlamp,,saidcmeans including, means to vary the potential at s'aidotherdterminal between two fixed Po i ev a r 2 Ni e ana am swin i -ticombination, ingia filing. potential andan in zi praete nae'd range of IV I I conne'cted to one terminal of sa dlglo'w lampfwhich periodicallyan amount guishing potential and the maximum firing potential, and meansfor applying a unidirectional potential to the other terminal of saidglow lamp, said means including means to vary the potential at saidother terminal between a first fixed potential level which provides amaximum difie ence of potential at the terminals of the glow lamp ofless than the minimum firing potential and a second fixed potentiallevel which provides a difference of potential at the terminals of theglow lamp which varies from a value greater than the maximum firingpotential to less than the minimum extinguishing potential.

3. Visual signal apparatus comprising in combination, a transistorhaving an output electrode, load circuit means connected to said outputelectrode including a load resistor and a first source of unidirectionalelectrical energy in series, means for indicating an electricalcondition in said load circuit means comprising a glow discharge lamphaving a firing potential and an extinguishing potential within apredetermined range of values, and an energizing circuit for said lampincluding, in series, said load resistor, said lamp and a source ofperiodically varying electrical energy having a polarity opposite tothat of the potential drop across said resistor produced by the currentflowing through said output electrode and varying an amount greater thanthe diflference between the minimum extinguishing potential and themaximum firing potential of said predetermined range.

4. Visual signal apparatus comprising in combination, a glow dischargelamp having a firing potential and an extinguishing potential within apredetermined range of values, a first source of unidirectionalpotential connected to one terminal of said glow lamp, the potential ofsaid first source varying periodically an amount greater than thedifference between the minimum extinguishing potential and the maximumfiring potential of said predetermined range, an energizing circuit forsaid lamp including in series, a second source of unidirectionalpotential, a

load resistor, and a transistor, said load resistor and the outputelectrode of said transistor being connected to the other terminal ofsaid lamp, and means for selectively operating said transistor toproduce current flow through said load resistor, said operation of saidtransistor providing at the output electrode two fixed levels ofpotential, a first fixed level when current is flowing which provides amaximum difference of potential across the glow lamp of less than theminimum firing potential and a second fixed level when no current isflowing which provides a difference of potential at the terminals of theglow lamp which varies from a value greater than the maximum firingpotential to less than the minimum firing potential.

5. Visual signal apparatus comprising a glow discharge lamp having afiring potential and an extinguishing potential within a predeterminedrange of values, an energizing circuit for said lamp including aresistor and a source of periodically varying electrical energy inseries, said source having a potential which varies an amount greaterthan the difierence between the minimum extinguishing potential and themaximum firing potential of said predetermined range, and means forcontrolling the potential across the lamp including circuit means forconducting a current through said resistor to produce a potential dropthereacross of a polarity and magnitude effective to reduce the maximumpotential available at the lamp below the potential required to fire thelamp, and means for selectively stopping the current conduction throughsaid circuit means to shift the potential available at the lamp so thatit varies between the minimum extinguishing voltage and maximum firingvoltage of said predetermined range.

References Cited in the file of this patent UNITED STATES PATENTS2,772,410 Logue et al. Nov. 27, 1956

